With the rapid industrialization and the explosive growth in the number of motor vehicles in recent years, air pollutions become increasingly severe. In China, the concentration of tiny particulates, particularly fine particulates (each having an aerodynamic equivalent diameter equal to or smaller than 2.5 micro meter, also known as PM2.5), as dominant atmospheric pollutants in the atmosphere, has been continued at a high level since early 2013. The hazy weather has significantly increased and people's health and daily lives are in serious danger. There is thus a need for a detection device for detecting concentration of tiny particulates.
Currently, there have been a number of methods for detecting tiny particulates in the air, including for example quartz oscillating microbalance method, beta ray method and light scattering method. Most of these methods require an inertial impactor as a front-end device for separating tiny particulates from larger particulates. As an example, Patent Document CN102680349A discloses a PM2.5 monitoring device equipped with an inertial impactor. Although the inertial impactor works well in size separation, its high cost, large dimension and precise control of air flow rate limit its application in home scenarios.
On the other hand, deposition methods have been used conventionally for detecting size distribution of particulates in liquid phase. As an example, Patent Document JP2011179862 discloses a method for calculating sedimentation velocity of particulates in liquid phase. Although there is also a deposition process for particulates in the air, it is very different from the deposition process in liquid phase. The viscosity of air is much lower than that of liquid and thus the Brownian dispersion in the air cannot be neglected. Since the Brownian dispersion is sensitive to many factors such as concentration gradient, temperature and particulate size, it is difficult to detect the size distribution of suspended particulates in the air precisely using the deposition methods.